Endocrine studies in cystinosis: compensated primary hypothyroidism.

Children with nephropathic cystinosis exhibit marked growth retardation. Improved medical management and renal transplantation have increased their life expectancy beyond the second decade. We have studied endocrine function in seven patients with cystinosis and reviewed autopsy findings of four patients and medical records of 24 others. One 10-year-old boy was overtly hypothyroid. The six other patients had normal studies of peripheral thyroid function but two had borderline and two had frankly elevated serum TSH levels. Stimulation tests of cortisol and growth hormone secretion and basal levels of serum NSILA-s were normal. Postmortem histology of the thyroid glands revealed extensive destruction and infiltration of the epithelium with cystine crystals. Despite the presence of cystine crystals in other endocrine tissues, there was no destruction of epithelium in glands other than in the thyroid. We conclude that in nephropathic cystinosis "compensated" primary hypothyroidism occurs frequently and early and may be diagnosed by measurement of serum TSH concentrations.